Imbedding mass for dental purposes



Patented Sept. 22, 1936 UNlTED STATES.

2,054,894 nunnnnma MASS FOR DENTAL PURPOSES Werner Busch, Dormagen,

and Paul Wolski.

Leverkuaen-Wiesdorf, Germany, assignors to Winthrop Chemical Company, Inc., New York, N. Y., a corporation of New York No Drawing.

Application November 27, 1933,

%?! No. 700,020. In Germany December 1,

5 Claims. (Cl. 222-488) This invention relates to an imbedding mass for dental purposes which is characterized by yielding dental molds of high power of thermal expansion and of sufliciently great hardness, par- 6 ticularly in the heated state of the mold.

The known imbedding masses for dental purposes merely consist of a mixture of plaster of Paris and quartz-like materials, such as sand, silica, kaolin and the like. Apart from a great 10 fineness of the mass which is necessary to obtain a a smooth surface of the mold a power of thermal expansion as high as possible, and a sufficiently great hardness, particularly when the mold is heated to the casting temperature, are required I especially when the molds are intended for the manufacture of gold casts. The high power of thermal expansionis necessary to compensate the contraction of the gold after the cast has been made; the great hardness of the mold is so required to avoid brittling and the deformation of the mold when the heavy liquid gold flows in.

The imbedding masses hitherto known and marketed yield molds which possess the high power of thermal expansion and a great hardness 26 simultaneously only to an unsatisfactory extent. The power of thermal expansion may be increased in a known manner by adding a greater percentage of the quartz-like material to the imbedding mass, however, the solidity and stability of the 80 mold is strongly diminished by such a procedure. On the other hand, an increase of the contents of plaster of Paris by which a greater solidity is attained unfavorabiy influences the power of thermal expansion. For the said reasons it has 35 hitherto been impossible to prepare molds for dental purposes which yield unobjectionable and undamaged casts which do not show the effect of the contraction of the casting material. Wearisome experiments have been made to com- 40 pensate the contraction of casting material by utilizing a certain expansion of the wax model while imbedding the wax model at elevated temperature. Such procedure, however, is practically very unsatisfactory.

The present invention provides for an imbedding mass which yields molds displaying simultaneously high power of thermal expansion and great hardness, so that the contraction of the casting material is compensated during the manufacture of the cast, and undamaged casts are obtained. 7

In accordance with the present invention an imbedding mass yielding the said dental molds of high power of thermal expansion and great hard- 55 ness is obtainable by evenly distributing in the effects.

hitherto customary imbedding masses, mainly consisting of plaster of Paris and a quartz-like material, a relatively small percentage of a solid organic acid, such as citric acid, tartaric acid, oxalic acid, succinic acid, gluconic acid, benzoic '5 acid, salicylic acid and naphthoic acid. Relatively small quantities of the organic acids are requiredto bring about the above described Preferably the said substances are added in a percentage of about 1% or less, but it may 10 be mentioned that also 5% may be added without any remarkable disadvantage. The said organic acids may be used in admixture with each other. The addition of the said organic acids causes the great hardness and favorably l6 influences the expansion of the mass.

The new imbedding mass characterized by the contents of the solid organic acids may contain other additions usual in the manufacture of imbedding masses, for instance, substances, which accelerate the solidification of the mold, such as potassium chloride and potassium sulfate, sodium chloride and sodium sulfate, potassiumaluminium sulfate; or retarding additions, for instance, borax, in order to regulate the setting time of the imbedding mass as desired. Other customary additions ar for instance, coloring substances, in onder to better differentiate the imbedding mass from other substances.

It may be mentioned that an imbedding mass yielding molds of particularly favorable properties as to solidity and expansion are obtainable when using instead of the alabaster plaster of Paris, customary in such imbedding masses, wholly or partially a semi-hydrate gypsum which is obtainable by heating natural gypsum in a closed vessel at an elevated pressure. and which is characterized by a particularly high shaking weight, for instance, a shaking weight loosely put in of above 0.9 g./ccm. and shaken in of above 1.45 an/com. and a strewed in quantity" of more than'230 grams of the plaster of Paris,

the said strewed in quantity" being defined as that quantity of a gypsum which, when strewed into 100 cos. of water, still yields a mass which is capable of being poured. The method of determinating the "shaking weight (sometimes also called weight by volume") loosely put in" and shaken in" is the usual one. The gypsum is poured into a funnel with a sieve placed therein, and runs into a vessel of a content of 1 liter. The height and the diameter of the vessel are in a proportion of 2:3. The gypsum beyond the rim of the container is removed by striking. During this operation any shaking of the container is to be avoided. The content of the container is then weighed. The weight in kg. per liter determines the shaking weight "loosely put in. If the content of the container is shaken during the running of the gypsum from the funnel until the container is completely filled so that no more gypsum may be added and the gypsum beyond the rim of'the container is again removed by striking, the container then gives the shakin weight shaken in.

The molds obtainable by means of the above described imbedding masses permit in a very simple manner the manufacture of dental casts, forinstance, gold casts, which practically do not show any deviation from the model since the molds prepared from the new imbedding mass compensate the normal contraction of the cast material in view of their high thermal expansion during the casting process. It is obvious that this simple means for avoiding the breaking of the mold and the contraction of the cast constitutes a remarkable advance in the manufacture of dental casts.

The invention is further illustrated by the I following example, but it is not restricted thereto.- I

Example-30 parts by weight of a semi-hydrate gypsum of good quality are well mixed with 65 parts by weight of finely ground quartz sand, 0.2 parts by weight of citric acid, 02 parts by weight of oxalic acid, and 0.1 part by weight of potassium sulfate; An imbedding mass is thus obtained which yields in a favorable setting time (about 15-20 minutes) molds of greatsolidity in the' heated state and of a high power of thermal expansion which practically compensates the contraction of gold (amountingto-about 1.3% in a linear direction) when cooledfrom the melting temperature to normal temperature. I I

In the above case the semi-hydrate gypsum is preferably wholly or partially a gypsum having a shaking weight"loosely put in of above 0.9 and fshak'en in of above 1.45 and a. strewed in quantity" of about 230 grams. For instance, the use of a mixture of 10 parts by weightof the normal alabaster plaster of Paris andabout parts by weight of the semi-hydrate gypsum having the properties above specified has proved to be very favorable. E

The addition of potassium sulfate usedas an accelerator for the solidification of the mold may be omitted, but also larger quantities of, for instance, 0.2 grams or of other accelerators mentioned above may be employed.

We claim:--

1. An expansive imbedding mass for dental purposes, comprising plaster of Paris and a finely dividediquartz-like material, which imbedding mass is characterized by the content of a slight percentage of a solid organic carboxylic acid sufilcient to give the mass an acid reaction when mixed with water.

2. An expansive imbedding mass for dental purposes, comprising plaster of Paris and a finely divided quartz-like .material, which imbedding mass is characterized by the content of a slight percentage of. a solid organic polycarboxyllc acid suihcient to give the mass an acid reaction when mixed with water.

3. An expansive imbeddins mass for dental purposes, comprising plaster of Paris and a finely divided quartz-like material, which imbedding mass is characterized by the content of a'slight percentage of oxalic acid sufiicient to give the mass an acid reaction when mixed with water.

4. An expansive imbedding mass for dental purposes, comprising plaster of Paris and a iinely divided quartz-like material, which imbedding mass is characterized by the content of a slight percentage of oxalic and citric acid sufficient to give the mass an acid reaction when mixed with water.

5. An expansive imbedding mass for dental purposes, comprising about 60 parts by weight of fine quartz, sand, about parts by weight of a semi-hydrate-gypsum, about 0.2 parts by weight of citric acid and 0.2 parts'by weight of oxalic acid, said imbedding mass givingan acid reaction when mixed with water.

a WERNER BUBCH.

PAUL WOIBKI. 

